Locator spring structure for contact assembly of high voltage electrical circuit breakers

ABSTRACT

An electrical circuit breaker or isolator, intended to carry high currents of the order of 100,000 amperes, has for each pole a respective moving contact assembly comprising a plurality of parallel-connected movable contact arms each carrying a respective movable contact, said arms being of strip metal, to reduce manufacturing costs, are disposed side-by-side and substantially parallel in a carrier, each said arm being mounted in the carrier by a respective locator spring shaped to provide a loading portion which engages one longitudinal edge of the arm and a pair of limbs extending across the arm one adjacent each side thereof and which locates on a cross-member, extending transversely of the arms, of the carrier adjacent the other longitudinal edge of the arm, the locator springs serving yieldingly and resiliently to mount the movable contact arms in the carrier and the limbs of the springs effectively locating the arms relative to one another.

United States Patent [191 Kidd 51arch 20, 1973 [54] LOCATOR SPRINGSTRUCTURE FOR 2,933,580 4/1960 Watson ..200/8 A x CONTACT ASSEMBLY OFHIGH 2,945,927 7/1960 Mason ..200/8 A x I l E BREAKERS Appl. No.:184,800

Foreign Application Priority Data Oct. 22, 1970. Great Britain..50,094/70 US. Cl. ..200/166 R, 200/166 BF, 200/166 E Int. Cl. ..H0lh1/50, H0lh 9/30 Field of Search ..200/8 A, 11 G, 11 H, 11 K, 200/11 J,166 R, 166 E, 166 BE, 166 BF,

References Cited UNITED STATES PATENTS 9/1954 Kuhn et a] ..200/166 R XJones ..200/166 BF Primary Examiner-J. R. Scott Attorney-Kenwood Ross etal.

[57] ABSTRACT An electrical circuit breaker or isolator, intended tocarry high currents of the order of 100,000 amperes, has for each pole arespective moving contact assembly comprising a plurality ofparallel-connected movable contact arms each carrying a respectivemovable contact, said arms being of strip metal, to reduce manufacturingcosts, are disposed side-by-side and substantially parallel in acarrier, each said arm being mounted in the carrier by a respectivelocator spring shaped to provide a loading portion which engages onelongitudinal edge of the arm and a pair of limbs extending across thearm one adjacent each side thereof and which locates on a cross-member,extending transversely of the arms, of the carrier adjacent the otherlongitudinal edge of the arm, the locator springs serving yieldingly andresiliently to mount the movable contact arms in the carrier and thelimbs of the springs effectively locating the arms relative to oneanother.

6 Claims, 4 Drawing Figures PATENTEDHAR201915 SHEEI 10F 3 INVENTOR; ALANLISTER KIDD evfimwwciwe ATTORNEYS.

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ALAN LISTER KIDD ATTORNEYS.

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LOCATOR SPRING STRUCTURE FOR CONTACT ASSEMBLY OF HIGH VOLTAGE ELECTRICALCIRCUIT BREAKERS This invention concerns electric circuit breakers andisolators and more particularly contact arrangements thereof.

It is well known, in relation to electric circuit breakers, that aso-called blow-off force occurs at the abutting contacts, when currentis passing therethrough, tending to separate such contacts, and thisforce is proportional to the square of the current passing. Accordingly,with circuit breakers of large short circuit current capacity, eg of theorder of one hundred thousand peak amperes, provision has to be made tocounteract very substantial blow-off forces to keep the movable contactsproperly in engagement with their stationary contacts.

For this reason, as well as others, it is advantageous to provide, foreach pole of the circuit breaker, a moving contact assembly comprising aplurality of parallelconnected movable contact arms or fingers eachcarry ing a respective movable contact engageable with a fixed contact,so that the current in each pole is split according to the number ofarms. The total blow-off force then arising for any particular currentis reduced in inverse proportion to the number of such arms, as comparedwith the case where only a single contact arm is present, andconsequently the actuating mechanism and structure of the circuitbreaker needs only to apply a substantially smaller force to retain themovable contacts in their closed position, without blow-off occurring.

In such an assembly, it is usual to load the individual contact arms bymeans of respective helical compression springs. Such an arrangement hasthe disadvantage, however, that it restricts the minimum width ofmovable contact arm which can usefully be employed, and consequentlyrestricts the number of such arms which can be incorporated in aparticular assembly of predetermined dimensions. In practice, if oneattempts to make use of movable contact arms of width less thanfive-sixteenths of an inch, one is confronted with the difficult problemof designing corresponding helical springs able to apply adequate forceto the respective arms without either the spring rate being too high orthe length being too great. Accordingly, in the heretofore proposedconstructions, the movable contact arms have usually been thick, tofacilitate spring loading thereof, and the number of such arms whichhavebeen employed in any specific assembly has been small.

An object of the present invention is to provide a parallel-connectedmovable contact arrangement of the above-mentioned kind, which isparticularly suitable for electric circuit breakers but may also beemployed in electrical isolators, wherein relative location of andloading of the arms within a carrier therefore is achieved in a simpleand convenient manner which permits the arms to be substantially thinnerthan has previously been necessary, so that a large number thereof canbe employed.

With this object in view, the present invention provides an electriccircuit breaker or isolator which has, for the or each pole thereof, arespective moving contact assembly comprising a plurality ofparallel-connected movable contact arms each carrying a respectivemovable contact engageable with a fixed contact, characterized in thatthe arms are of strip metal, are disposed side-by-side and substantiallyparallel in a carrier, each the arm being mounted in the carrier by arespective locator spring which is shaped to provide a loading portionwhich engages one longitudinal edge of the arm and a pair of limbsextending across the arm one adjacent each side thereof and whichlocates on a cross member, extending transversely of the arms, of thecarrier adjacent the other longitudinal edge of the arm.

In such arrangement, the locator springs serve yieldingly andresiliently to mount the movable contact arms in the carrier, and thespace between adjacent pairs of the contact arms has one limb of thelocator spring of each of the arms extending therethrough, so that theselimbs serve effectively to locate the arms relative to one another.

Each locator spring is conveniently substantially rectangular inconfiguration, with its shorter sides constituting the limbs, one of thelonger sides being the loading portion of the spring, and the otherlonger side incorporating a formation whereby it locates on the crossmember.

The formation whereby the spring locates on the cross member may be aneye; and such eye can be formed by oppositely directed hooks provided onthe two ends of a single spring-wire length forming the locator spring.

The aforementioned one of the longer sides of the locator spring whichprovides the loading portion of the spring is conveniently shaped sothat only a short central portion engages with the respective edge ofthe respective contact arm.

Each movable contact arm is conveniently in the form of a metalpressing, the respective movable contact being secured adjacent one endthereof, e.g. by high speed brazing which can be effected withoutsoftening the contact arm.

Each such arm may then be formed with a V-shaped notch adjacent itsother end whereby it locates onto an arcuate surface provided by a fixedhinge contact block to which the carrier is hingedly connected.

The end of each movable contact arm adjacent which the respectivemovable contact is provided is conveniently shaped to provide aprotrusion beneath which engages a lip of the carrier whereby to limitpossible movement of the arms under the loading of their springs.

The invention will be described further, by way of example, withreference to the accompanying drawings which illustrate a preferredembodiment thereof, as applied to an electric circuit breaker, it beingunderstood that the following description is illustrative and notlimitative of the scope of the invention.

In the drawings:

FIG. 1 is a cross-section through a preferred embodiment of electriccircuit breaker conforming to the invention showing one contact assemblythereof;

FIG. 2 is a plan view of the contact assembly of FIG.

FIG. 3 is a cross-section on the line 3-3 of FIG. 2; and

FIG. 4 is a cross-section on the line 4-4 of FIG. 2.

The preferred embodiment of the circuit breaker conforming to theinvention is a three pole breaker and comprises a generally, rectangularcasing (indicated generally at moulded from a suitable electricallyinsulating plastics material the interior of which is divided byappropriate partitions (not shown) to provide three channels (not shown)each of which accommodates a respective contact assembly 11. A manualoperating mechanism (not shown) of the breaker includes a pivoted leverprojecting through a top cover of the casing 10 and connected to thecontact assemblies 11 by way of a toggle linkage 12 incorporating amember (not shown) which is supported by a pivoted trip bar (not shown)extending transversely across the three channels. A respective bimetaland electromagnet arrangement (not shown) associated with each contactassembly cooperates with the trip bar to pivot the latter, uponoccurrence of a sustained overload (i.e. a sustained passage of currentin excess of the rated current of the circuit breaker) or uponoccurrence of short circuit conditions (i.e. the passage ofa currentsubstantially in excess of the rated current), to release its supportand permit collapse of the toggle linkage 12 and thereby trip thebreaker.

The contact assemblies 11 in each of the three channels aresubstantially identical, and therefore it is only necessary to describeone of them in detail.

Such contact assembly 11 comprises, at one end of the channel, a fixedcontact block 13 having a fixed contact strip 14 secured to its uppersurface so as to extend transversely across the channel. In the otherend of the channel is mounted a hinge contact block 15 whose end 16closest to the fixed contact block 13 has bores 17 at each side thereofeach being about three quarters of an inch long and extendingtransversely of the channel and is shaped on its upper surface toprovide a substantially semi-cylindrical upwardly directed bearingsurface 18 disposed so that its axis extends transversely of the channelsubstantially concentrically of the bores 17.

The bores accommodate respective hingep pins 19 the ends 20, 21 of whichprotrude from the hinged contact block 15 and serves pivotally toconnect to said hinge contact block 15, an inverted-U-sectioned, orinverted-channel-sectioned movable contact arm carrier 22, with the ends20, 21 of the pins 19 engaging into apertures 23, 24 in respective sidewalls 25, 26 of said carrier 22.

The carrier 22, which is connected to the toggle linkage 12, serves tocarry a plurality of parallel movable contact arms 27 which, in theclosed condition of the breaker illustrated in FIG. 1, extend from thehinge contact block 15 to just above the fixed contact block 13, so thatmovable contacts 28 carried by each of said arms 27 engage with arespective location on the fixed contact strip 14 on the fixed contactblock 13.

There are thirteen of said movable contact arms 27 of which the middleone 270 (see FIG. 4) is longer than the rest, has its own movable arcingcontact 29 offset relative to the others, and is spring loaded downwardsrelative to the carrier 22 by an independent helical spring 30 set intothe carrier 22. Each of the movable contact arms 27 is in the form of ametal pressing, of copper strip, for example of approximatelythree-sixteenths of an inch in thickness, generally rectangular inconfiguration, and having the respective movable contact 28 secured toone edge thereof, adjacent to one end, e.g. by high speed brazing.Adjacent to the other end, each such strip has a V-shaped notch 31 cuttherein, from the same edge, whereby the arm 27 locates on and makeselectrical contact with the bearing surface 18 of the hinged contactblock 15. The fact that the movable contacts 28 can be secured to theirrespective arms 27 by high speed brazing has the advantage that it canbe effected without causing the material of the arm 27 to anneal andbecome soft. Any softening of the movable contact arms 27 is to beavoided, of course, since impacts of substantial force occur in theoperation of the breaker, and this would cause distortion of the arms27.

About midway along the length of the carrier 22, a cross member 32thereof extends transversely across the carrier 22 between the sidewalls 25, 26 thereof at a level below the lower edges of the contactarms 27, which lower edges are, of course, the edges in which theV-shaped notches 31 are provided and on which the movable contacts 28are secured. The arms 27 are mounted in the carrier 22 by way ofrespective locator springs 33 which engage with the upper edges of therespective contact arms 27 and locate on the cross member 32.

Each locator spring 33 (see FIGS. 3 and 4) is made from a length ofstrong spring wire bent to a substantially rectangular configuration.One of the longer sides thereof is a loading portion 34 which isslightly bowed along its length and provides a linear middle section 35which abuts against a part of the upper edge of the respective contactarm 27 The two shorter sides of the spring constitute guide limbs 36, 37which extend across the respective contact arm 27 one against each sideof the contact arm 27 and join with the other longitudinal side of thespring which is provided with a formation 39 locating the spring 33 onthe cross member 32 of the carrier 22. The formation 39 is provided bythe ends of the length of wire, which ends are curved to form oppositelydirected hooks 40, 41 which together form an eye around the cross member32.

Each said one end of each contact arm 27 is formed with a protrusion 42which engages with a lip 43 on the carrier 22 to limit movement of thearm 27 under the influence of its spring 33.

It will be appreciated that the circuit breaker effectively operates inthe same way as prior known comparable constructions of breaker. Withthe operating handle in the on" position, the toggle linkage 12 isextended to press the carriers 22 downwards, so that the movablecontacts 28 all engage the fixed contact strip 14 and are loadedthereagainst by their respective locator springs 33.

The moving contact arms 27 in the contact assembly of each pole serve todivide the current passing in said pole, with the consequent advantageof reduced blowoff force (as already discussed herein) so that the forcenecessary to hold the moving contacts 28 in adequate engagement with thefixed contact strip 14 is substantially less than in the case where eachpole has a smaller number of contact arms 27 and respective-movablecontacts 28, and the components of the circuit breaker can be of lesserdimensions and strength than in the latter instance.

Upon occurrence of a sustained overload or short circuit (as aboveexplained) the toggle 12 is broken, the arms 27 are displaced away fromthe fixed contacts 14 to open the circuits through the circuit breaker,and the handle is moved to the tripped position.

In the addition of the advantages already discussed and the advantagethat the circuit breaker may be constructed with components of lesserdimensions and/or strength, as discussed in the foregoing, theconstruction of the invention has other advantages. Thus, thearrangement of springs 33 providing for one limb 36, 37 thereofalongside each side of the respective contact arm 27 achieves properlocation of the contact arms 27 relative to one another, so that theylie side-by-side in parallel disposition in a very simple and convenientmanner which is easy to assemble. Furthermore, the form of the contactarms 27 is such that they can be manufactured readily and relativelyinexpensively by simple pressing operations as compared with theexpensive castings or extruded sections which have hitherto beenconventionally employed for movable contact arms.

It is to be understood that the invention is not confined to the precisedetails of the foregoing example, and variations may be made to thesedetails without departing from the scope of the invention. Thus, forexample, the contact arrangement 1 1 of the invention can be employed inan electrical isolator, the construction being such as to provide twoopposed carriers 22 with their contact arms 27 facing one another toprovide therebetween a gap for accommodating a withdrawable conductorleading, for example, to an electrical component, the arrangement beingsuch that relative movement between the contact arms 27 and theconductor is possible for withdrawing the latter to isolate theelectrical component.

What we claim is:

1.- In an electrical circuit breaker or isolator, thecarrier, thecarrier having a cross-member extending transversely of and spaced fromone side of the contact arms, each contact arm constituting a strip inelectrical contact with the contact block adjacent one of its ends, asingle loop helical locator spring serving to mount each contact arm inthe carrier, the locator spring having its ends engaged with thecross-member of the carrier and extending around the contact arm andhaving a loading portion extending diagonally across a longitudinal edgeof the contact arm and having limbs extending one adjacent each side ofthe contact arm, the loading portion of the locator spring biassing thearm towards the cross-member and the limbs acting as spacers betweenadjacent contact arms.

2. In the circuit breaker as claimed in claim 9 wherein each locatorspring is substantially rectangular in configuration, with its shortersides constituting the limbs, one of the longer sides being the loadingportion of the spring and the other longer side incorporating aformation whereby it locates on the cross-member.

3. In the circuit breaker as claimed in claim 2, wherein the formationis an eye formed by oppositely directed hooks provided on the two endsof a single springl-wire length formin the locator spring.

4. n the circult brea er as claimed in claim 2 wherein the said onelonger side of the locator spring is shaped whereby only a short centralportion engages with the respective edge of the respective contact arm.

5. In the circuit breaker as claimed in claim 4 wherein each movablecontact arm is formed with a V- shaped notch adjacent its other endwhereby it locates onto an arcuate surface provided by a fixed hingecontact block to which the carrier is hingedly connected.

6. In the circuit breaker as claimed in claim 1 wherein the said one endof each movable contact arm is shaped to provide a protrusion beneathwhich engages a lip of the carrier whereby to limit possible movement ofthe arms under the loading of their spring.

1. In an electrical circuit breaker or isolator, the combination of: acarrier, a hinge contact block, a plurality of parallel movable contactarms mounted in the carrier, the carrier having a cross-member extendingtransversely of and spaced from one side of the contact arms, eachcontact arm constituting a strip in electrical contact with the contactblock adjacent one of its ends, a single loop helical locator springserving to mount each contact arm in the carrier, the locator springhaving its ends engaged with the cross-member of the carrier andextending around the contact arm and having a loading portion extendingdiagonally across a longitudinal edge of the contact arm and havinglimbs extending one adjacent each side of the contact arm, the loadingportion of the locator spring biassing the arm towards the crossmemberand the limbs acting as spacers between adjacent contact arms.
 2. In thecircuit breaker as claimed in claim 9 wherein each locator spring issubstantially rectangular in configuration, with its shorter sidesconstituting the limbs, one of the longer sides being the loadingportion of the spring and the other longer side incorporating aformation whereby it locates on the cross-member.
 3. In the circuitbreaker as claimed in claim 2, wherein the formation is an eye formed byoppositely directed hooks provided on the two ends of a singlespring-wire length forming the locator spring.
 4. In the circuit breakeras claimed in claim 2 wherein the said one longer side of the locatorspring is shaped whereby only a short central portion engages with therespective edge of the respective contact arm.
 5. In the circuit breakeras claimed in claim 4 wherein each movable contact arm is formed with aV-shaped notch adjacent its other end whereby it locates onto an arcuatesurface provided by a fixed hinge contact block to which the carrier ishingedly connected.
 6. In the circuit breaker as claimed in claim 1wherein the said one end of each movable contact arm is shaped toprovide a protrusion beneath which engages a lip of the carrier wherebyto limit possible movement of the arms under the loading of theirspring.